This artist drawing of a Block III GPS satellite orbiting the Earth. China is now the third country to develop its own GPS satalite system, called the 'Big Dipper.'

Photo Illustration/Lockheed Martin/AP

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Beijing — Something important was missing from all the fanfare here surrounding Tuesday’s announcement that China had launched a homegrown satellite navigation system to rival the US Global Positioning System (GPS): any mention of what it is really for.

“The driver for this program is that it is a strategic imperative” for China’s military modernization, says Eric Hagt, an expert on China’s space activities at the Center for Defense Information in Washington.

You would not have learned that from the head of the China Satellite Navigation Office, Ran Chengqi, who announced that the Beidou system, which means “Big Dipper” in Chinese, had gone live.

The Beidou system, however, is clearly designed to do more than keep an eye on the government carpool, foreign analysts say. A sophisticated positional navigation system is essential to pinpoint enemy ships and to guide missiles with precision, Mr. Hagt points out. The newly launched system, he adds, “is a guarantee for the Chinese that they would have an independent system in place” in case of conflict.

Until now, the Chinese military has relied on GPS. But that is controlled by the US government, which could block Beijing’s access if it wanted to, effectively blinding China’s Army, Navy, and Air Force.

For the moment, the 10 Beidou satellites offer positioning, navigation, and timing services over most of China and the whole of Southeast Asia, Mr. Ran said. The launch of six more satellites next year will extend Beidou’s reach to most of the Asia Pacific region and improve its accuracy to GPS levels. The system is expected to go global in 2020.

Tuesday’s announcement makes China the third nation in the world with its own satellite navigation system, after the US and Russia, whose Glonass satellites are fully operational. The European Union plans to make its own Galileo system operational by 2019.

Like GPS, Beidou will be free, Ran says, hoping that Chinese and foreign companies will build and sell cheap receivers to use its information. Also like GPS, Beidou is thought to have an encrypted military channel, offering more precise information to those that control it, though Ran made no mention of this.

US firms already use GPS alternatives for some purposes; Apple’s iPhone 4S relies on Glonass as well as GPS for its location feature, for example. How widely used Beidou will be by civilian clients, however, is unclear.

“How many people would trust the Chinese over the US or the EU to keep a public channel open if it was not in their interests?” Hagt wonders. “I don’t know if people would have the same confidence.”